The invention relates to a communication or data exchange method for use in connection with a decentralized bus system, in particular a field bus, which can be employed in the automation of technical processes. A plurality of communication participants are connected to the bus system, including at least two active communication participants (“masters”) and at least one passive communication station (“slave”).
An active communication participant is a communication participant in a bus system which can autonomously initiate a communications operation. In contrast, a passive communication participant always requires an external stimulus, in order to place data on the bus. One example of such an external stimulus is a send request from a master.
Each master is assigned to a different master system. The master systems, per se, have no physical manifestation. Rather, the term “master system” is used to describe a configured relationship between an active communication participant and the passive communication participant(s) assigned to it. Namely, the master systems determine the possibility or impossibility of certain communication relationships between the communication participants connected to the bus system. Under the communication relationships defined by the master systems, every message (including a data part and a header part) transmitted over the bus is detected, at least by the slave, which evaluates at least certain data of the message header. When the message header data matches entries stored in a filter table, the slave makes the data of the message available to its application.
The so-called cross-terminal traffic communication or data exchange method improves communication between the participants connected to the field bus. According to the cross-terminal traffic method, data can be exchanged, for example, directly between passive communication stations, (or “slaves”), despite the fact that the communication protocol defined for the field bus, on its face, permits no direct communication relationship between such passive communication members. Prior to development of the cross-terminal traffic method, communication between two passive communication stations had always required an intermediary, in the form of an active communication party (or “master”), and proceeded as follows. A first communication relationship is established between a first passive communication party and a master, and the data is transferred from the first slave to the master. Next, the master establishes a communication relationship with a second passive communication party, and the data is transferred from the master to the second passive communication party, the desired recipient.